Setting Definition Query on ArcPy layer from shapefile for ArcMap

Question

I am trying to determine options to set a layer definition query using ArcPy.

I know that it is possible when using arcpy.mapping.ListLayers().

However, in this scenario I am loading in shapefiles, and using arcpy.MakeFeatureLayer_management() in ArcPy.

How do I set a definition query on the layer that I create from using this geoprocessor?

I am using ArcMap 10.2.

Answer 1

The code below will create, from a shapefile, a layer file called test_A.lyr which has a Definition Query of "testField" = 'A' saved into it.

import arcpy

arcpy.MakeFeatureLayer_management(r"C:\temp\testLines.shp","test_lyr")
lyr = arcpy.mapping.Layer("test_lyr")
lyr.name = "test"
lyr.definitionQuery = '"testField" = ' + "'A'"
lyr.saveACopy(r"C:\temp\test_A.lyr")

del lyr

If required, you could also add this layer file,or the Layer object (lyr) from prior to it being saved as a layer file, into your map via arcpy.mapping.AddLayer.

To see whether a where_clause on MakeFeatureLayer gets passed through as a Definition Query, which I think is undocumented behaviour, I performed a second test below to verify the Answer of @John, and he is quite correct.

arcpy.MakeFeatureLayer_management(r"C:\temp\testLines.shp","test_lyr2",'"testField" = ' + "'A'")
lyr2 = arcpy.mapping.Layer("test_lyr2")
lyr2.name = "test2"
lyr2.saveACopy(r"C:\temp\test_2.lyr")

del lyr2

Answer 2

Yes, it should definitely be possible for you as that is what the optional "where_clause" parameter is for - see its documentation for details and examples, but basically you just need to include the definition query as the where_clause param and it should work. Only thing to note, if you are using a layer that doesn't have an ObjectID/FID field, ArcGIS has issues running SQL expressions against it, but any regular ArcGIS layer will.

Answer 3

If you are loading layers into Arcmap using the MakeFeatureLayer geoprocessing tool, you can set the definitionQuery on existing arcmap layers using the arcpy.mapping class layers - definitionQuery.